1. Field of the Invention
The present invention relates to a robot control system provided in a machining system including a robot and a machine tool.
2. Description of the Related Art
In a machining using a machine tool, it is desired to make the machine tool operate for twenty-four consecutive hours in order to raise the operation rate of the machine tool. To this end, it is required that an operator performing operations for feeding an unprocessed workpiece to the machine tool (i.e., a loading operation) and removing a processed workpiece from the machine tool (i.e., an unloading operation) works for a long time. However, a machining job site where the machine tool is used may be in a hostile environment in which droplets of cutting oil used for a machining and chips produced in the machining are suspended. Further, in the operations for feeding and removing the workpiece, carrying a heavy workpiece by a manual-handling or using a crane, etc., is dangerous for the operator. Therefore, instead of making an operator perform loading and unloading operations for a long time, an industrial robot (hereinafter referred simply to as a robot) sometimes performs loading and unloading operations.
A machine tool or a robot, used for a machining, is controlled by a controller. A controller for a typical machine tool, such as a lathe, a machining center, etc., is referred to as a machine tool controller or a CNC (computer numerical control) unit, whereas a controller for a robot is referred to as a robot controller. In a dedicated machine tool designed for a specific application, a PLC (programmable logic controller) may be used as a controller. Such a controller is typically provided with a display and/or a control panel, used by an operator for operating the machine tool or teaching the robot. In the machine tool controller, the display and/or the control panel may be installed fixedly at the front side of the machine tool, so as to allow the operator to visually check a machining condition. On the other hand, in the robot controller, a portable teaching unit or teach pendant, capable of being carried by an operator, may be provided as the display and the control panel. Further, both in the machine tool controller and the robot controller, an object to be displayed on the display of the controller or operated through the control panel of the controller may be limited to the machine tool or robot to be controlled by the controller.
In a machine tool assumed to be used in combination with a robot, it is known that a wall surrounding a working space for a machining is provided with a safety door allowing an operator to enter the inside of the wall and another safety door allowing a robot enter the inside of the wall and perform loading and unloading operations of a workpiece. For example, Japanese Patent No. 3379115 (JP-B-3379115) describes a machine tool provided with a front door allowing an operator to perform certain work and a side door allowing a transfer robot to carry a workpiece in and out, separately with each other.
In the case where a configuration disclosed in JP-B-3379115 is used for a system in which a robot performs loading and unloading operations, it is required to design a new machine tool or modify an existing machine tool in a way as to provide a safety door for an operator and another safety door for allowing a robot to carry a workpiece in and out. On the other hand, even in the case where a robot and a machine tool are used in combination, it is preferable to permit an existing machine tool, designed on the assumption that loading and unloading operations are manually performed, to be used in situ. In this case, a robot feeding and removing a workpiece to and from the inside of a machine tool shares a single safety door with an operator performing certain work on the inside of the machine tool.
In the case where the robot and the machine tool are used in combination, in order to prevent the operating robot from interfering with the operator of the machine tool, it is preferable to place a safety fence surrounding the operating range of the robot. Further, since the operator of the machine tool operates the machine tool at a location where the display and the control panel of the machine tool controller are installed, it is preferable to separate the installation location of the display and the control panel from the operating range of the robot by a safety fence.
However, since the display and the control panel of the machine tool controller may be installed near a safety door so as to permit the operator to visually check the conditions inside the machine tool, it may be difficult to separate the installation location of the display and the control panel from the operating range of the robot by a safety fence. Consequently, the safety fence may be configured to entirely surround the machine tool and the operating range of the robot, so as not to permit the operator to enter the inside of the safety fence during the operation of the robot. In this configuration, in order to check the condition of the machine tool or change the setting of the machine tool during the operation of the robot, the robot is temporarily stopped, and thereafter, the safety fence is opened and the operator manipulates the control panel of the machine tool controller installed inside the safety fence. Further, in order to prevent the robot from moving while the safety fence is opened and the operator manipulates the control panel of the machine tool controller installed inside the safety fence, the system is configured such that a safety plug is provided so as not to permit the safety fence to be closed while the operator is inside the safety fence and an interlock as a safety circuit is provided so as not to permit the robot to start the operation while the safety fence is opened.
In order to perform certain work using the display and/or the control panel of the machine tool controller during the operation of the robot, the robot is first stopped, and then the safety fence is opened and the operator enters the inside of the safety fence to perform the works, which deteriorates working efficiency. Further, in a configuration wherein a single robot performs the loading and unloading operations for a plurality of machine tools, if the robot is stopped and the safety fence is opened for the manipulation of the control panel of any one of machine tool controllers, the loading and unloading operations for the machine tool controlled by another machine tool controller are also stopped. Thus, if the safety fence is frequently opened or closed, the production efficiency of the machine tool will be deteriorated.
One exemplary work performed by an operator using the control panel of the machine tool controller is a work wherein the machining accuracy of a workpiece is determined after a machining is completed and the given parameter of the machine tool is changed based on a determination result. This work is performed, after an event such that a tool is replaced by new one, the lot of unprocessed workpieces is changed, a tooling change is carried out for new workpieces, etc.; at a time when the machining is restarted after a prolonged arrest; every time a predetermined number of machining operations has been performed; and so on. If the machining accuracy of the workpiece after the machining is completed, determined by the operator, does not reach an allowable value, the operator manually inputs correction data in relation to a tool length, a tool diameter or a machining position on the workpiece, set in the machine tool controller, so as to improve the machining accuracy. Alternatively, based on the result of a visual inspection of a machining quality of the machined workpiece, the operator may increase or decrease the rotation speed of a spindle or the feed speed of a tool, so as to improve the machining quality. In order to manipulate the control panel of the machine tool controller inside the safety fence, as described above, the operator temporarily stops the robot, opens the safety fence, manipulates the control pane of the machine tool controller, and thereafter, restarts the operations of the machine tool and the robot, which deteriorates the production efficiency.
Another exemplary work performed by an operator using the control panel of the machine tool controller is a recovery work as being performed at a time when the machine tool stops due to a minor factor. If the display of the machine tool controller is far away from the safety fence and the operator thus cannot visually check the display from the outside of the safety fence, it is difficult to determine whether a malfunction or an alarm (or warning) occurs in the machine tool or not, or whether the machine tool operates normally or not. When the alarm occurs in the machine tool, a tool is first retracted by a retracting operation toward a safe position where the tool does not interfere with a workpiece, the content of the alarm is checked, necessary measures are taken to dissolve a reason for the alarm, and thereafter, the tool is returned to a machining position to restart the machining. However, in the case where the machine tool is stopped due to the minor factor, it may suffice that the alarm is reset and the machining is restarted. It is the cause of a deterioration in working efficiency that, in order to determine the reason for the alarm and control the retracting and returning motion of the tool, the robot is temporarily stopped, the safety fence is opened, the control panel of the machine tool controller is manipulated, and thereafter, the operations of the machine tool and the robot are restarted, every time the machine tool stops, regardless of a reason for the stoppage of the machine tool. Further, another trouble may occur due to, e.g., an operational mistake in the restarting of the robot, and thereby, the stoppage of the machine tool due to the minor factor in nature may lead to the stoppage of the entire system which may take time for a recovery work.
A further exemplary work desired to be performed by an operator using the control panel of the machine tool controller is a work for checking the machining condition of the machine tool. This work is to check the existing machining condition, such as how many cycles of the machining program have been executed, how many percentages of an entire machining process have been completed, etc. Due to this checking work, it is possible to determine the residual necessary machining time and start a setup operation for a subsequent machining. However, opening the safety fence and stopping the robot, in order to perform the checking work, may deteriorate working efficiency.